There are many factors that determine the connection speed.  The drivers are not the major player.  The biggest factor is the telephone line, whether the actual line external to the residence or the internal wiring or telephone instruments.  e.g. some cordless phones can cause interference and slow down the connection speed.  A defective voice phone or answering machine can also affect the connection speed.  The internal wiring from the Telco interface (demarc) box external to the residence to the wall jack you are using for the modem can affect speed.  The RJ-11 cable between the modem and the telco jack can affect the speed.  Finally, the condition of the actual telephone line, the distance (number of hops) between the residence and the telco central office can affect it, etc.  Finally, the ISP's modems can be a slowdown point.